A conventional base station (BS) based radio access system is defined as communication between a BS or an equivalent of the BS and a mobile station (MS) and an MS which performs communication with a BS in a radio access system is controlled by the BS or the equivalent of the BS. Since the BS controls operations of all MSs according to a predetermined rule, efficiency may be deteriorated according to an application or a channel environment of an MS.
In a conventional BS based radio access system, a relay node (RN) may be considered for, for example, enlargement of high data rate coverage, improvement of group mobility, temporary network deployment, improvement of cell edge throughput and/or provision of network coverage to a new area. An RN refers to a node for receiving a signal from a source node and transmitting the signal to a destination node. The RN may be more easily deployed than the base station. However, since the RN must be connected to the BS through a predetermined backbone network and does not have mobility, there are restrictions in terms of solving a shadow area and coverage extension.
In order to solve such problems, as a method of supporting high-rate data transmission, solving a shadow area and realizing coverage extension, a method of directly performing communication between MSs with good channel states has been studied. Up to now, as communication between MSs, a transmission scheme or a method of grouping MSs participating in communication between the MSs has mainly been studied. In particular, the majority of studies have proposed new transmission schemes with improved performance as compared to conventional schemes in a specific situation, but handover in communication between MSs has received little attention. In particular, unlike handover between BSs in a conventional BS based radio access system, handover between MSs needs to consider not only handover between an MS and a BS but also handover between MSs. Therefore, since handover between MSs is different from handover in a conventional BS based radio access system, there is a need for a new handover process.